This invention relates to a tamper resistant device for indicating the movement and/or position of a closure means with respect to a frame surrounding the closure means to dependably indicate that the means is in the shut position.
Devices of this kind are generally known in a variety of designs and serve the purpose, for example, of centrally monitoring the particular positions of several successive doors forming a sluice gate system. This is to make sure that several doors are not unlatched simultaneously to provide access to an area to be secured and to guard against the possibility that despite proper actuation of the locking means a door remains in an open position.
For central monitoring of such sluice gate systems one possibility is to use video monitoring equipment. Apart from the fact that these equipments are relatively expensive, the cameras cannot be protected against unauthorized intervention. Also, the image reproduction equipments (viewers) overtax the monitoring personnel, especially if a large number of them must be watched simultaneously.
The attempt has also been made before to monitor the positions of doors of such sluice gate systems with magnetic contacts disposed on the door frames. By an iron plate correspondingly disposed on the door panel, the magnetic contacts can be activated, and thereby the closed position of the door panel can be signaled. However, with the aid of such an iron plate or of an object similar to it with comparable ferromagnetic properties this monitoring system is especially easy to outwit and a closed position of the door panel can be simulated without the actual open position of the door panel being perceivable in a central monitoring station.
Lastly a sufficiently reliable indication of the position of doors is not assured either with the aid of so-called rotary position indicators mounted on the door hinge plate, as they, too, cannot be sufficiently secured against tampering.